Transcript Tables in SNMP MIBs (3)

POSTECH DP&NM Lab
Real-time Streaming Protocol
(RTSP)
Byungchul Park
DPNM Lab., CSE, POSTECH
Email: [email protected]
2008. 6. 3
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Table of Contents
• Introduction
• RTSP Message
• RTSP Methods
• Existing Problems of RTSP
• MIB for RTSP
• Summary
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Introduction - Streaming
• What is Streaming?
– Streaming is the process of playing a file while it is still
downloading
– Streaming technology lets a user view and hear digitized
content – video, sound and animation – as it is being
downloaded
• Streaming breaks the data into packets with size
suitable for the transmission between server and
clients
• RTSP establish and controls streams
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Introduction - RTSP
• RTSP is an application level protocol for the control of
real-time streaming data with syntax and operations
similar to HTTP
• IEFT standard  RFC 2326 (April, 1998)
• RTSP uses RTP as the underlying data delivery
protocol and offers a VCR-like control to the user:
– PLAY, STOP, PAUSE, FF, REW
• RTSP = Network remote controller
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RTSP vs. RTP
• RTSP allows two-way communication
– Viewers can communicate with the streaming server and do
things like rewind the movie, go to a chapter, and so on
– It does not typically deliver the continuous streams itself
• RTP is one-way protocol
– Send live or stored streams from the server to the client
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RTSP vs. HTTP
• RTSP has similar syntax and operations with HTTP
• Both an RTSP server and client can issue requests
• An RTSP server needs to maintain state by default in
almost all cases, as opposed to the stateless nature
of HTTP
• Data is carried out-of-band by a different protocol
(RTP)
• RTSP has various methods while HTTP has only two
methods (GET, POST)
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Message Types
• RTSP is a text-based protocol and uses UTF-8
(Unicode octet) encoding
• Messages can be either requests or responses
• Request contain methods, the object the method is
operating upon and parameters to further describe
the method
• After receiving and interpreting request, the recipient
replies with a response message
• RTSP messages are based on HTTP messages, with
slight changes to allow for new status codes and
different primitives
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RTSP Message
• RFC 2616 - HTTP/1.1
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RTSP Methods
Method
Direction
Requirement
Description
DESCRIBE
C->S
recommended
Get description of media object
ANNOUNCE
C->S, S->C
optional
Change description of media object
GET_PARAMETER
C->S, S->C
optional
OPTION
C->S, S->C
required
Get available methods
PAUSE
C->S
recommended
Halt delivery, but keep state
PLAY
C->S
required
Start playback
RECORED
C->S
optional
Start recording
REDIRECT
S->C
optional
Redirect client to new server
SETUP
C->S
required
Establish transport
SET_PARAMETER
C->S, S->C
optional
Device or encoding control
TEARDOWN
C->S
required
Remove state
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Protocol State Machines
• The RTSP client and server state machines describe
the behavior of the protocol from RTSP session
initialization through RTSP session termination
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Problems of Current Protocol
• NAT Traversal problem
• The RTSP protocol says nothing about the problems
of recovering state over machine or software failure
• Quality problem
• Insufficient functionalities
• No billing infrastructure: pay-per-play?
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NAT Problem (1/3)
• What is NAT (Network Address Translator)?
– Translate private IP address to public IP address
– Acts as a firewall
[출처] NAT란??|작성자 야쿨트
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NAT Problem (2/3)
• What makes the problem?
• Server behind NAT
– Client can not access the server
• Client behind NAT
– Client can access the server however server may not
respond to client (RTP)
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NAT Problem (3/3)
• Possible Solution?
– MMUSIC WG working on ICE + RTSP
– Skype Protocol
• MMUSIC (Multiparty Multimedia Session Control)
– ICE (Interactive Connection Establishment)
– ICE is designed for RIP’s NAT traversal
– Work on mapping ICE to RTSP
• Skype Rendezvous-Relay Service
– Skype works well on every NAT environment and firewall
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Recovering State over Machine (1/2)
• State Machine
??
PAUSE
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Recovering State over Machine (2/2)
PAUSE
PLAY, PAUSE,
RECORD
RECORD
PLAY
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Quality Problem (1/2)
• In case of network congestion or packet loss
– RTSP will cause part of the stream to be lost.
– That's how RTP (the underlying conveyance protocol)
behaves, as it uses UDP
– RTP is the de facto standard protocol to carry real-time
delay-sensitive payloads such voice over IP
– With voice calls, people definitely prefer to loose some audio
frames that have to wait a few seconds for the network to
recover and retransmit
– With video on demand, people may well prefer to wait a
while for the audio/video buffers to refill
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Quality Problem (2/2)
• It’s not RTSP’s problem. This problem caused by
– Lack of QoS management mechanism (IPv4)
– Underlying conveyance protocol is RTP (UDP)
• What could be a solution?
– IPv6?
– There’s no certain solution for QoS problem
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Insufficient Functionalities (1/2)
• Suppose your VCR
–
–
–
–
–
–
Play a video
Pause
Stop
FF
RWD
Record
• RTSP
–
–
–
–
Play a video
Pause
TearDown (Stop)
Record
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Insufficient Functionalities (2/2)
• The authors are lacking experience with RECORD
• Seem to need significant clarification on how to use it
• Issues related to RECORD are:
–
–
–
–
–
–
How to use ANNOUNCE
How to signal “Disk Full” or “Quota Reached”
SETUP requirements to be able to RECORD
Appending, replacing
Creation of new files and there status
Recording and watching is not possible
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No Charging Infrastructure (1/2)
• There are many commercial products that employ
RTSP
– Real Player (www.real.com/player)
– Cisco Application Control Engine (ACE)
(http://www.cisco.com/en/US/prod/collateral/modules/ps2706
/ps6906/prod_bulletin0900aecd8045859e.html)
– Nokia5300
– Unlimited TV On PC (www.thecomputertv.com)
– Application Streaming (www.thinstall.com)
– Free Premium TV for PC (www.PremiumTVforPC.com)
– PlayBox Technology (www.playbox.tv)
– Etc.
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No Charging Infrastructure (2/2)
• Contents providers or service providers may need
charging infrastructure for their revenues in short time
• Possible charging scheme
–
–
–
–
Pay-per-playing
Pay-per-duration
Pay-per-packet
Flat-rate
• At least usage data should be kept for charging
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MIB for RTSP
• There’s no MIB for RTSP
• MIB for RTSP should contain
–
–
–
–
–
–
–
–
–
–
–
Client’s IP address
# of Packets
# of Octets
Client’s Tool
Start time
End time
Playing time
# of lost packets
Accessed media
Disk space for recording
Etc.
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Summary
• RTSP provides an extensible framework to enable
controlled, on-demand delivery of real-time data
• This protocol is intended to control multiple data
delivery sessions, provide a means for choosing
delivery channels, and provide a means for choosing
delivery mechanisms based upon RTP
• There’s no security vulnerability
• However, this protocol has some possible problems
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Question?
?
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